We bought our first generator for motorhome power in 2019, a shiny 3,000-watt portable unit that the dealer swore would handle everything we needed. Three days into our first dry camping trip in Arizona, we were sitting in 95-degree heat with a dead air conditioner and a generator for motorhome use that kept tripping its breaker every time we tried to run the microwave. We returned it, ate the restocking fee, and spent another $800 on a bigger unit. That one lasted six months before the inverter failed. By the time we figured out what we actually needed, we had burned through over $3,000 in returns, repairs, and bad advice. Looking back now, we wish we had understood the basics of RV power requirements before making that first purchase, because choosing the right generator for motorhome living makes all the difference between comfortable boondocking and constant frustration.
The problem was not the generators themselves. The problem was that we had no idea how much power our rig actually pulled, and we trusted people who did not know either.
Most RV dealers will tell you that a 3,500-watt portable generator handles a 30-amp motorhome fine. That is technically true if you are only running one major appliance at a time. But the moment you try to make coffee while the air conditioner is cycling, or run the microwave while charging your laptop, you are going to trip the breaker or overload the unit. We learned this the hard way in a Walmart parking lot at 11 PM when our generator shut down mid-dinner and would not restart until it cooled off for an hour.
There are three types of generators that matter for RV use: portable inverter generators, built-in onboard units like the Onan 5500, and conventional portable generators. Inverter generators are quieter and produce cleaner power, which matters if you are running sensitive electronics like laptops or CPAP machines. Built-in units are convenient because they are permanently installed and run on your RV’s propane or diesel fuel, but they cost a fortune to replace and can be a nightmare to service. Conventional portables are cheaper and more powerful, but they are loud, heavy, and produce power that can fry your electronics if the voltage regulation is poor.
What we needed, and what we eventually bought, was a 4,500-watt inverter generator that could handle our air conditioner, microwave, and coffee maker all running at the same time without breaking a sweat. It cost us $1,200, which felt like a lot until we realized we had already spent more than that on units that did not work. If we had done the math before our first purchase, we would have saved ourselves a year of frustration and a pile of wasted money.
The Math That Finally Made Sense (And Why We Almost Skipped It)
We are not math people. We avoided the wattage calculations for months because it felt like homework, and we wanted to buy something that worked. But once we sat down and actually added up the numbers, it took about ten minutes and explained everything that had gone wrong.
Here is how it works. Every appliance in your RV has a wattage rating, usually printed on a label somewhere on the back or bottom. Our air conditioner pulls 1,800 watts when it is running, but it needs about 3,000 watts for the first three seconds when the compressor kicks on. That starting surge is what kills undersized generators. Our microwave is rated at 1,000 watts, and our coffee maker pulls another 900. If we try to run all three at once, we need at least 5,700 watts of starting power, which is way more than the 3,000-watt generator we bought could handle.
The difference between running watts and starting watts is the key to understanding why generators fail. Running watts are what the appliance uses once it is up and running. Starting watts, also called surge watts, are what it needs for that first split second when the motor or compressor kicks in. Air conditioners, refrigerators, and anything with a compressor or motor will have a starting wattage that is 1.5 to 2 times higher than the running wattage. If your generator cannot handle that surge, it will trip the breaker or shut down to protect itself.
We finally figured this out after calling an RV tech who walked us through the math over the phone. He told us to add up the running watts of everything we wanted to run at the same time, then multiply the highest starting wattage by 1.5 to account for the surge. That number is the minimum generator size we needed. For us, that was 4,500 watts. Anything smaller was not going to cut it.
Why Portable Generators Lost Us Money, and When They Actually Make Sense
Portable generators are overrated for full-time RVers. We said it. If you are living in your motorhome and dry camping more than a few days a month, a portable unit is going to cost you more in fuel, maintenance, and hassle than it is worth. They are loud, they take up storage space, and you have to haul them out and set them up every time you need power. We got tired of that routine after about three months.
That said, portables make perfect sense if you are a weekend camper or if you need backup power for emergencies. They are cheaper than built-in units, easier to repair, and you can use them at home during a power outage. If you are only camping a few weekends a year, a portable generator for motorhome trips is a solid choice. Don’t expect it to replace shore power if you are boondocking for weeks at a time.
Our Two Generators That Actually Survived Four Years on the Road
We have owned six generators since 2019. Four of them failed, broke down, or annoyed us so much that we sold them. Two of them are still with us, and we trust them enough to take them into the desert for weeks at a time with no backup plan.
The first one is a 4,500-watt inverter generator that we bought in 2021 after our second unit died. We will not name the brand because we are not getting paid to promote it, but we will say it is not a Honda and it cost us about $1,200. It has run our air conditioner in 110-degree heat in Death Valley, powered our space heater in 20-degree cold in Colorado, and kept our refrigerator running during a three-week stretch in Utah when we were completely off-grid. The only time it almost failed was in New Mexico when we ran it for eight hours straight without letting it cool down. It started overheating and the oil light came on. We shut it down, let it sit for an hour, and it fired right back up. We learned to give it a break every four hours after that.
The second one is a built-in Onan 5500 that came with our current motorhome. We did not want it at first because we had heard horror stories about Onan generators overheating and shutting down with error codes. But ours has been rock solid, mostly because we figured out the ventilation issue before it became a problem. A lot of RV manufacturers install these units with terrible airflow, and the generator overheats after 30 minutes and shuts down with a code 36 error. We have met other RVers who had to cut ventilation holes in their generator compartment themselves because the factory did not do it right. One couple we camped with in Arizona had to run their generator with the access panel open to keep it from overheating. That is insane for a $3,000 piece of equipment.
We checked our ventilation as soon as we bought the rig, and sure enough, the airflow was restricted. We drilled two extra vent holes in the compartment, and the generator has run flawlessly ever since. It is quiet enough that we can hold a conversation ten feet away from it, and it runs on propane so we do not have to carry extra gas cans. The downside is that if it ever dies, we are looking at a $3,000 replacement cost, which is why we keep the portable as a backup.
The Champion we tried in 2020 was loud enough to wake up half the campground. The Westinghouse we bought in 2019 died after six months and the warranty process was a nightmare. The cheap Harbor Freight Predator 3500 that everyone raves about online ran our air conditioner for about nine hours on a tank of gas, but the build quality felt flimsy and we did not trust it for long-term use. The Honda generator for motorhome use that we tested was bulletproof and whisper-quiet, but it cost $1,300 for a 2,200-watt unit, which was not enough power for our needs. We would have had to buy two and run them in parallel, which would have pushed the cost over $2,600. That was more than we wanted to spend.
The Generator for Motorhome Setup We Wish We Had Known About Before Day One
The first time we set up our portable generator, we parked it too close to the motorhome and filled the cabin with exhaust fumes. We woke up at 2 AM with headaches and had to open every window and run the roof vents for an hour to clear the air. Carbon monoxide is no joke, and we got lucky that night. Now we set the generator at least 20 feet downwind from the RV, and we bought a battery-powered CO detector that we keep near the floor where the fumes settle.
We also learned the hard way that you have to run your generator at least once a month, even if you are not using it. We let ours sit for three months one winter, and when we tried to start it in the spring, the carburetor was gummed up with old fuel. We had to take it to a small engine shop and pay $150 to have it cleaned out. The mechanic told us that ethanol fuel goes bad in about 30 days, and if it sits in the carburetor, it turns into a varnish that clogs everything. Now we run the generator for 20 minutes every month, even when we are plugged into shore power, to keep the fuel flowing and the engine lubricated.
We also stopped using fuel stabilizer after our mechanic told us it was mostly snake oil. He said the best way to keep fuel fresh is to use it, not to add chemicals. We run our generator for motorhome power often enough that the fuel never sits long enough to go bad, and we have not had a carburetor problem since. If you are going to store your generator for more than a month, drain the fuel completely. Do not add stabilizer and hope for the best.
Before You Buy: The One Question That Changes Everything
Here is the question that will tell you what size generator for motorhome power you actually need: Will you boondock for more than three days at a time, more than once a month?
If the answer is no, buy a 3,500-watt portable inverter generator and call it a day. You can find a decent one for under $800, and it will handle your air conditioner, your microwave, and your basic electronics without breaking a sweat. You will have to refuel it every six to eight hours, but if you are only using it on weekends, that is not a big deal. Make sure it is an inverter model with low total harmonic distortion, because the cheap conventional generators will fry your laptop and your phone chargers. We have learned plenty of other boondocking tips and safety practices over our years on the road that have kept us safe and comfortable off-grid.
If the answer is yes, and you are planning to spend weeks at a time off-grid, you need at least a 4,500-watt unit or a built-in generator like an Onan 5500. The portable will give you flexibility and redundancy, but the built-in will save you the hassle of setting up and tearing down every time you move. We run both, and that setup has kept us powered through four years of full-time travel without a single night where we had to pack up and find shore power.
If you are looking at generator for motorhome options and you are not sure whether to go portable or built-in, ask yourself this: Do you want convenience or do you want a backup plan? Built-in generators are convenient until they break, and then you are stuck paying $3,000 for a replacement and waiting weeks for a service appointment. Portables are a pain to set up, but if they fail, you can replace them for $1,200 and be back in business the same day. We have both because we have been burned by both, and we are not willing to trust our power supply to a single point of failure anymore.
The generator for motorhome power that almost killed our trip in Arizona in 2019 taught us that lesson. We were three days into a two-week boondocking stretch when our only generator died, and we had to drive 60 miles to the nearest town to find a replacement. We lost two days of our trip and spent $900 we had not budgeted for. Now we carry a backup, and we have never had to cut a trip short again.
